Engines may use cam switching systems to adjust valve lift of gas exchange valves in the cylinders. For example, cam lobes coupled to an engine cam shaft may have different lift profiles, such as full lift, partial lift, or zero lift. For example, such engines may incorporate cam profile switching (CPS) to enable high or low lift valve train modes which correspond to increased fuel efficiency during high and low engine speeds, respectively. As another example, e.g., by switching to a zero lift profile, engine cylinders may be deactivated during operation modes with decreased engine output in order to increase fuel efficiency.
As described for example in U.S. Pat. No. 7,404,383, an engine may include a camshaft with multiple outer sleeves containing lobes splined to a central cam. By engaging a pin into a grooved hub in each sleeve, the axial position of the sleeve can be repositioned so that a different cam lobe engages a roller finger follower (RFF) of a valve.
Various actuator and groove configurations are known for these types of valve switching mechanisms. In one approach for a two step system, a two-pin actuator may interface with a Y-groove to allow shifting of the sleeve in either direction depending on its starting point. One type of actuator may allow both pins to deploy when energized unless the pin is physically blocked because no groove is under it. After a pin has sufficiently extended, the actuator can be de-energized, and the pin will remain extended until the groove depth is reduced, pushing it back to the home position, where it remains until the actuator is again energized.
The inventors herein have recognized that, in approaches which activate both pins, a timing window may exist where the actuator can be energized until the intended pin deploys in its groove, then the actuator must be de-energized before the other pin falls into the unintended groove which it passes over as the sleeve moves. If the actuator is not de-energized in time, the second pin could fall in the groove causing a mechanical interference. This mechanical interference would likely result in substantial damage to the system. Previous solutions using the Y-mechanism for a two-step shifting sleeve camshaft have used actuators with individual control of the pins. However, having individual control of the pins typically requires two coils per actuator as well as twice as many control signals from the engine control module, thus increasing costs associated with such systems.
In one example approach, in order to address these issues, a method for a multiple-lift profile cam lobe switching mechanism actuator in an engine comprises deploying a first pin into a groove of a camshaft outer sleeve while a second pin remains in place due to an absence of a groove in which to deploy, and maintaining the second pin in place with a ball locking mechanism even after the second pin is exposed to a vacated groove in the camshaft outer sleeve.
In this way, a second pin may be prevented from deploying after the first (intended) pin has deployed by using a mechanical locking mechanism within the actuator, so that the second pin does not fall into the unintended groove which it passes over as the sleeve moves. Further, in such an approach, only a single coil may be used to actuate both pins, leading to potential reduction in costs associated with additional actuators and control mechanisms.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.